Galaxy Zoo is an online citizen science project: people, any people, can look through vast numbers of pictures of galaxies, classifying them. Spirals, irregulars, ellipticals: with a little training (provided by the site itself) it's easy, and as it turns out, hugely addicting to do.

A young Dutch woman named Hanny van Arkel was combing through Galaxy Zoo images one day and found a spiral galaxy, but next to it was a weird, green smear of light. What was it? She tagged it and asked around, and the mystery deepened. It was real, but odd. What could it be?

Astronomer Bill Keel wondered as well. He got time on Hubble to observe this strange object, now called Hanny's Voorwerp (which is Dutch for "thing"), and now we think we know what it is: a huge cloud of gas, as big as our own Milky Way, lit up by the nearby spiral! Every galaxy has a supermassive black hole in its core, and as material falls in it heats up and emits huge amounts of light. Some of this light coming from the galaxy's core hit the Voorwerp, causing it to glow. The thing is, the galaxy's black hole is no longer emitting this light! At some point, the material falling in must have run out, shutting off the light switch. But the gas in the Voorwerp is still glowing; it takes a long time for that material to fade away. It's been about 200,000 years or so, which is a long time for us humans, but is the blink of an eye in the life of a galaxy.

Long enough, of course, for Hanny to find it. And oh, did I mention that Hanny, a musician, found out about Galaxy Zoo because Brian May, of the rock group Queen, blogged about it? Yup. She wasn't an astronomy enthusiast before all this, yet now she has an object named after her, and the knowledge that Hubble was pointed at a target because of something she just up and decided to do. If there's a life lesson in this, feel free to figure it out for yourself.